Ferrofluid seal apparatuses are known for sealing rotary shaft elements, such as for use as an exclusion-type seal or as a pressure capacity-type seal. Such ferrofluid seal apparatus provides an effective seal between different environments, either at the same or at different pressures or having the same or different environments.
U.S. Pat. No. 4,293,137, issued Oct. 6, 1981, relates to the use of a ferrofluid seal apparatus which comprises a single axial permanent magnet in the shape of a flat washer element surrounding a rotatable shaft; and which flat washer element captures ferrofluid on the inside or outside diameter of the washer element. The flat washer element provides a ferrofluid seal between a housing and the exterior surface of the washer element or between the interior surface of the washer element and a rotatable shaft surface. In addition, such axial polarized permanent magnets are also employed to seal hermetically on one or both sides of a ball bearing.
A multiple-stage pressure capacity-type ferrofluid seal apparatus is described, for example, in U.S. Pat. No. 3,620,584, issued Nov. 16, 1971, which patent describes a multiple-stage ferrofluid seal apparatus employing an annular permanent magnet and a plurality of separate spaced apart ferrofluid O-ring seals extending about the surface of the shaft element to be sealed, each seal providing its own defined pressure capactiy and employing two pole pieces, one on either side of the annular, axially polarized, permanent magnet.
In addition, magnetic bearing systems, such as a ball bearing, have been used to support a rotary shaft and to permit the low friction rotation thereof and have employed ferrolubricants retained with the confines of the inner and outer race of the ball bearing assembly, such as, for example, described in U.S. Pat. No. 3,977,739, issued Aug. 31, 1976.
British Pat. No. 783,881, published in October of 1957 relates to a magnetic seal wherein a plurality of axially stacked separate magnetic seals are placed about a rotary shaft to form a plurality of magnetic barriers or seals about the rotary shaft. The seal, so prepared, comprises a plurality of separately stacked, axially polarized, permanent magnets and separate pole pieces to form a multiple-stage, pressure capacity-type seal.
It is desirable to provide a pressure capacity-type ferrofluid seal apparatus which is more compact than conventional, mulitple-stage ferrofluid seal apparatus, and which seal apparatus may be constructed at lower cost with the use of lower magnetic energy product and yet have the same or substantially more pressure capacity, as required in the prior art ferrofluid seal apparatus.